Document conveying devices and image reading devices comprising such document conveying devices

ABSTRACT

A document conveying device includes a conveying path and a feed unit. The feed unit includes a tray including a document positioning surface configured to receive documents thereon, in which the document positioning surface has a hole formed therethrough. The feed unit also includes a separation roller which is rotatably supported by a drive shaft extending in a direction orthogonal to a document conveying direction and is configured to contact an uppermost document of the documents and to separate and convey the uppermost document. The separation roller includes a first end and a second end opposite the first end. Moreover, the feed unit includes a document sensor including a detection portion configured to detect the documents and to selectively move between a first position in which the detection portion projects from the document positioning surface via the hole and a second position in which the detection portion is retracted from the document positioning surface via the hole. In addition, the feed unit includes a casing pivotably mounted on the drive shaft. The casing includes a plate extending adjacent to the first end of the separation roller in the document conveying direction, and the first end of the separation roller and the detection portion are positioned closer to the second end of the separation roller than the plate of the casing.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent Application No. 2007-311201, which was filed on Nov. 30, 2007, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to document conveying devices and image reading devices which comprise such document conveying devices. In particular, the present invention is directed towards document conveying devices and image reading devices which comprise such document conveying devices in which the document conveying device is configured to prevent or substantially prevent a conveyed document from becoming jammed independent of a thickness and independent of a rigidity of the conveyed document.

2. Description of the Related Art

A known image reading device, such as a copier device or a scanner device, or both, of a single-function or a multi-function device, is configured to read images from documents, and includes a document conveying device, such as an automatic document feeder (“ADF”). In the ADF, a document is conveyed and then is read by a stationary image reader.

A known ADF includes a plurality of document sensors for detecting a document, and the document sensors are arranged along a document conveying path. For example, in Japanese Unexamined Patent Application Publication No. 2007-223703, a separation roller, which is configured to convey documents one by one from a feed tray to a reading unit, is positioned facing the feed tray, and a pair of identical document sensors are positioned at an upstream side and a downstream side, respectively, of the separation roller. The document sensor at the upstream side is configured to detect whether a document is positioned on the feed tray, and the document sensor at the downstream side is configured to detect the leading end or the trailing end of a document fed toward the reading unit by the separation roller.

Each of the document sensors has a detection portion which is configured to project upward through a hole formed in the bottom of the feed tray that defines a conveying path. A lower portion of the detection portion acts as a shield between a light-emitting portion and a light-receiving portion of a photo interrupter. The detection portion is biased upward to be configured to project upward through the hole. The bias force is selected, such that the detection portion readily may be withdrawn, i.e., retracted, into the hole when a document contacts the detection portion. When a document causes the detection portion to pivot and retract into the hole, the pivoting of the detection portion is detected by the photo interrupter.

In the known ADF, when a document is positioned on a feed tray, the center line of the document generally is aligned with the center line of the feed tray. Consequently, the separation roller and a casing covering the separation roller generally are provided at the center position in the width direction of the feed tray, e.g., a direction orthogonal to the document conveying direction. Therefore, if the document sensors are positioned outside of the casing which covers the separation roller, a document may become jammed adjacent to the separation roller, especially when the conveyed document is thinner and has less rigidity than a predetermined type of recording medium, such as copy paper. In detail, referring to FIG. 8, when a document G2 is a relatively thin paper with a relatively low rigidity, the document G2 may not cause a detection portion 141 projecting from a document positioning surface 114 c of a feed tray 114 to retract sufficiently into a hole 122. Consequently, the thin-paper document G2 is lifted upward along the detection portion 141, and thus, may get caught by peripheral components, such as a drive shaft 131 of a separation roller 130, which may result in jamming of the document G2, i.e., a paper jam.

SUMMARY OF THE INVENTION

Therefore, a need has arisen for document conveying devices and image reading devices which comprise such document conveying devices which overcome these and other short comings of the related art. A technical advantage of the present invention is that the document conveying device is configured to prevent or substantially prevent a conveyed document from becoming jammed independent of a thickness and independent of a rigidity of the conveyed document.

According to an embodiment of the present invention, a document conveying device comprises a conveying path and a feed unit. The feed unit comprises a tray comprising a document positioning surface configured to receive at least one document thereon, in which the document positioning surface has a hole formed therethrough. The feed unit also comprises a separation roller which is rotatably supported by a drive shaft extending in a direction orthogonal to a document conveying direction and is configured to contact an uppermost document of the at least one document positioned on the document positioning surface and to separate and convey the uppermost document along the conveying path in the document conveying direction. The separation roller comprises a first end and a second end opposite the first end. The feed unit further comprises a document sensor comprising a detection portion configured to detect the at least one document positioned on the document positioning surface, and to selectively move between a first position in which the detection portion projects from the document positioning surface via the hole and a second position in which the detection portion is retracted from the document positioning surface via the hole. Moreover, the feed unit comprises a casing pivotably mounted on the drive shaft. The casing comprises a plate extending adjacent to the first end of the separation roller in the document conveying direction, and the first end of the separation roller and the detection portion are positioned closer to the second end of the separation roller than the plate of the casing.

According to another embodiment of the present invention an image reading device comprises a document conveying device. The document conveying device comprises a conveying path and a feed unit. The feed unit comprises a tray comprising a document positioning surface configured to receive at least one document thereon, in which the document positioning surface has a hole formed therethrough. The feed unit also comprises a separation roller which is rotatably supported by a drive shaft extending in a direction orthogonal to a document conveying direction and is configured to contact an uppermost document of the at least one document positioned on the document positioning surface and to separate and convey the uppermost document along the conveying path in the document conveying direction. The separation roller comprises a first end and a second end opposite the first end. The feed unit further comprises a document sensor comprising a detection portion configured to detect the at least one document positioned on the document positioning surface, and to selectively move between a first position in which the detection portion projects from the document positioning surface via the hole and a second position in which the detection portion is retracted from the document positioning surface via the hole. Moreover, the feed unit comprises a casing pivotably mounted on the drive shaft. The casing comprises a plate extending adjacent to the first end of the separation roller in the document conveying direction, and the first end of the separation roller and the detection portion are positioned closer to the second end of the separation roller than the plate of the casing.

Other advantages of the present invention will be apparent to persons of ordinary skill in the art in view of the following detailed description of the invention and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and the needs satisfied thereby, reference now is made to the following descriptions taken in connection with the accompanying drawings.

FIG. 1 is an external perspective view of an image reading device comprising a document conveying device, according to an embodiment of the invention.

FIG. 2 is an external perspective view of the image reading device of FIG. 1, in which a first cover is in an open position.

FIG. 3 is a plan view of the image reading device of FIG. 1, in which a second cover is removed.

FIG. 4 is a cross-sectional view of the image reading device of FIG. 1 taken along line IV-IV of FIG. 3.

FIG. 5 is an enlarged, cross-sectional view of the image reading device of FIG. 1 taken along line V-V of FIG. 3.

FIGS. 6A and 6B are a schematic, cross-sectional view of the image reading device of FIG. 1 taken along line VIa-VIa of FIG. 3.

FIGS. 7A and 7B are a schematic, cross-sectional view of a separation roller and a detection portion of an image reading device, according to another embodiment of the invention.

FIG. 8 is a schematic view of a separation roller and a detection portion of a known image reading device.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention may be understood by referring to FIGS. 1-7B, like numerals being used for like corresponding parts in the various drawings.

Referring to FIGS. 1-6B, an image reading device 2 according to an embodiment of the present invention is depicted. The image reading device 2 may be a reading unit of a single-function device which is configured to perform one of a facsimile function, a copier function, a printer function, and a scanner function, or a reading unit of a multi-function device (“MFD”) which is configured to perform at least two of a facsimile function, a copier function, a printer function, and a scanner function, or any combination thereof. The image reading device 2 may comprise a document conveying device 1.

The image reading device 2 may be positioned at an upper portion of the main body of the multi-function device. The image reading device 2 may comprise a first cover 4 mounted on the uppermost surface thereof, such that the first cover 4 is vertically pivotable about a hinge (not shown) positioned on the rear surface, e.g., the far side in FIG. 1, of the image reading device 2. The document conveying device 1 may be an automatic document feeder (“ADF”), and may be positioned on one side of the first cover 4, e.g., the left side in FIG. 1.

The front surface of the image reading device 2, e.g., the near side in FIG. 1, may comprise a control unit (not shown) which may comprise a panel display portion comprising a plurality of buttons, a plurality of switches, and a liquid crystal display used for performing various control operations. The image reading device 2, or a multifunction device comprising the image reading device 2, may be connected to an external device, such as a computer. Consequently, the image reading device 2 may be configured to operate in response to a command sent by a user via the control unit, or in response to a command output from the external device.

Referring to FIGS. 2 and 4, a rectangular transparent glass plate 5 and a transparent glass plate 6 that is oblong in an X-axis direction may be arranged side by side in the central area of a top surface which is exposed when the first cover 4 is in an open position. Specifically, the transparent glass plate 5 may be used to read a stationary document, and the transparent glass plate 6 may be used to read a document conveyed by the document conveying device 1. An image reader 7 may be positioned below the glass plates 5 and 6 in a reciprocable fashion in a Y-axis direction.

The image reader 7 may be a line image sensor which is configured to irradiate a document with light from a light source through the glass plate 5 or the glass plate 6, focus the light reflected from the document onto a light-receiving element through a lens, and convert the light to an electric signal. The image reader 7 is oblong and extends longitudinally in the X-axis direction in FIGS. 1 and 2, and may reciprocate in the Y-axis direction along a guide shaft (not shown) by a known moving mechanism. The image reader 7 alternatively may be a contact image sensor (“CIS”) or a charge coupled device (“CCD”).

When the image reading device 2 is a flat bed scanner (“FBS”) configured to read a stationary document positioned on the glass plate 5, the image reader 7 reads the document by moving in the Y-axis direction below the glass plate 5. A presser plate 8 may comprise a sponge or a whiteboard, and may be positioned on the undersurface of the first cover 4. The presser plate 8 may be configured to apply a force to a document toward the glass plate 5 when the first cover 4 is in a closed position and the document is positioned on the glass plate 5.

In contrast, when the document conveying device 1 is used in the image reading device 2, the document conveying device 1 conveys a document along a conveying path 13 while the image reader 7 positioned below the glass plate 6 reads the document. Specifically, in the document conveying device 1, the position of the glass plate 6 serves as a reading position of a reading unit 11. In the reading unit 11, the conveying path 13 allows a read face of a document to be exposed to the glass plate 6. In addition, the reading unit 11 may comprise a guide member 25 which is elastically biased to apply a force to the document toward the glass plate 6.

The document conveying device 1 may comprise a feed unit 10 which is configured to feed documents, the reading unit 11, and a discharge unit 12 configured to discharge documents after the reading unit 11 has read the documents. The reading unit 11 may be positioned at the lowest position, e.g., a position facing the glass plate 6, and the feed unit 10 may be positioned at a position above the discharge unit 12. Therefore, the conveying path 13 may be substantially U-shaped inside the document conveying device 1.

A second cover 16 may be positioned at the upper portion of the document conveying device 1. The second cover 16 may be configured to move between an open position and a closed position by pivoting about one side surface of the first cover 4, e.g., the left side in FIG. 1 and the right side in FIG. 4. The second cover 16 extends from the one side surface of the first cover 4 toward the central portion thereof, such that the tip end portion of the second cover 16 covers the downstream end of a feed tray 14 in the document conveying direction.

The feed unit 10 may comprise the feed tray 14 serving as a document stand and comprising a document positioning surface 14 c on which a plurality of documents to be fed may be positioned in a stacked manner. Because the document positioning surface 14 c of the feed tray 14 may be integrally connected to a component of the conveying path 13 in this embodiment, a downstream region of the feed tray 14 in the conveying direction also may be an upstream region of the conveying path 13.

The document positioning surface 14 c of the feed tray 14 may comprise a base end section and a free end section opposite the base end section. Specifically, the base end section may be proximate to one side of the first cover 4 on which side the document conveying device 1 is positioned, and the free end section may be inclined so as to be positioned above the base end section. In other words, a document may be positioned on the document positioning surface 14 c at an angle, such that the leading end of the document is positioned below the trailing end.

The base end section of the feed tray 14 may be covered by the second cover 16. The feed tray 14 may comprise a hinge 14 a at an intermediate section between the base end section and the free end section in the longitudinal direction of the feed tray 14. Thus, the free end section of the feed tray 14 may serve as a foldable portion 14 b which is pivotable about the hinge 14 a. Consequently, when it is not necessary to use the feed tray 14, the foldable portion 14 b of the feed tray 14 may be folded back to cover the document positioning surface 14 c of the feed tray 14, thereby preventing the document positioning surface 14 c from becoming dirty due to dust and foreign particles.

The feed tray 14 may comprise a pair of guide portions 20 configured to guide the side edges of a document. The guide portions 20 may be positioned, such that the distance therebetween in the X-axis direction is adjustable by a known interlocking mechanism 23. By moving the guide portions 20 manually, a center alignment operation may be implemented in which the center line of a document is aligned with the center line of the feed tray 14 in the width direction thereof, e.g., a direction orthogonal to the conveying direction.

The discharge unit 12 may comprise a discharge tray 15 on which a plurality of discharged documents may be positioned in a stacked manner. The discharge tray 15 may be formed planarly in the first cover 4 at a position below the feed tray 14, and may be separated from the feed tray 14 by a predetermined distance.

A plurality of rollers used for conveying a document may arranged at predetermined intervals in the conveying path 13. Specifically, the feed unit 10 may comprise a pick-up roller 34 and a separation roller 30, the conveying path 13 may comprise a conveying roller 35 positioned at an intermediate section thereof, and the discharge unit 12 may comprise a discharge roller 36. A driven roller 37 may be positioned facing the discharge roller 36. The number and arrangement of the rollers along the conveying path 13 may be modified.

In addition, document sensors for detecting a document may be arranged along the conveying path 13 at predetermined positions. Specifically, the feed unit 10 may comprise a document sensor 40 configured to detect whether a document is positioned on the feed tray 14. The conveying path 13 may comprise a document sensor 50 at an intermediate section thereof, which rotates in response to a document being conveyed in order to detect the leading end and the trailing end of the document. The document sensor 50 may be configured to detect the size of the document.

The separation roller 30 positioned in the feed unit 10 may be configured to convey a document positioned on the document positioning surface 14 c toward the reading unit 11. The separation roller 30 may be rotatably supported by a drive shaft 31 extending in a direction orthogonal to the conveying direction, and may be positioned above and facing the downstream region of the feed tray 14. The separation roller 30 may be aligned with a center line of the feed tray 14 in a direction which is orthogonal to the conveying direction, and may be unaligned with a center line of the feed tray 14 in the conveying direction. The dimension of the separation roller 30 in the width direction may be substantially shorter than the dimension of the feed tray 14 in the width direction. In other words, because a document is positioned on the feed tray 14 and the center line of the document is aligned with the center line of the feed tray 14 in the direction orthogonal to the conveying direction, the separation roller 30 may be allowed to properly contact the document independent of the size of the document.

The roller surface of the separation roller 30 may comprise a material that is elastically contactable with the document positioning surface 14 c of the feed tray 14. On the other hand, the portion of the document positioning surface 14 c which faces the separation roller 30 may comprise a separation pad 45 having a relatively high frictional resistance. Consequently, even when there are a plurality of documents stacked on the document positioning surface 14 c of the feed tray 14, the separation roller 30 may separate the uppermost document from the remaining documents with the frictional resistance, and may convey the separated document toward the reading unit 11.

The separation roller 30 may be covered with a casing 32 which is pivotably attached to the drive shaft 31. Similar to the separation roller 30, the casing 32 may be aligned with the center line of the feed tray 14 in the direction which is orthogonal to the conveying direction, and may be unaligned with the center line of the feed tray 14 in the conveying direction, and the dimension of the casing 32 in the width direction may be substantially shorter than the dimension of the feed tray 14 in the width direction. The casing 32 may have an arm-like shape which extends upstream in the conveying direction from the drive shaft 31. Moreover, the casing 32 may have an opening 33 formed therethrough, and the separation roller 30 may be exposed to the document positioning surface 14 c via the opening 33. In detail, the casing 32 may comprise an upper plate 32 a which covers the upper side of the separation roller 30, e.g., the side opposite to the side facing the document positioning surface 14 c, left and right side plates 32 b extending along the conveying direction, and a front plate 32 c which covers the front side of the separation roller 30, e.g., the downstream side of the separation roller 30 in the conveying direction. On the side of the casing 32 adjacent to the drive shaft 31, the lower edges of the two side plates 32 b may be positioned closer to the document positioning surface 14 c than the drive shaft 31. Moreover, the lower edges of the side plates 32 b may be curved upward toward the upstream side in the conveying direction so as to extend along the incline of the document positioning surface 14 c and to connect to the upstream-side edge of the upper plate 32 a.

The casing 32 may comprise a pick-up roller 34 rotatably attached thereto at a position upstream in the conveying direction relative to the separation roller 30. The pick-up roller 34 may be positioned such that its axis is parallel to that of the separation roller 30. The pick-up roller 34 may be linked to the separation roller 30 via a gear (not shown). When the separation roller 30 is rotated by the drive shaft 31, the pick-up roller 34 rotates in the same direction as the separation roller 30. With respect to the casing 32, the side thereof with the drive shaft 31 is a base end and the side thereof with the pick-up roller 34 attached is a free end. Consequently, because of the weight of the casing 32 and the pick-up roller 34, the pick-up roller 34 may contact the uppermost one of the documents positioned on the document positioning surface 14 c.

The document sensor 40 in the feed unit 10 may comprise a detection portion 41 which may be configured to project upward through a hole 22 in the document positioning surface 14 c of the feed tray 14, and a photo interrupter 42 that may be positioned within the document conveying device 1 and may be configured to detect a displacement of the detection portion 41.

The hole 22 in the document positioning surface 14 c may be located within the casing 32 for the separation roller 30. More specifically, the hole 22 may be located within a region covered by the upper plate 32 a of the casing 32, and may be sandwiched between the two side plates 32 b downstream of the pick-up roller 34 and upstream of the separation roller 30 in the document conveying direction.

Consequently, the upper side of the detection portion 41 projecting through the hole 22 may be covered by the casing 32. One of the side plates 32 b extends adjacent to one end of the separation roller 30 in the document conveying direction. The one end of the separation roller 30 and the detection portion 41 may be positioned closer to the other end of the separation roller than the one of the side plates 32 b. In other words, the one end of the separation roller 30 and the detection portion 41 may be positioned closer to the center line, parallel to the document conveying direction, of the feed tray 14 than the one of the side plates 32 b. In this embodiment, as shown in FIG. 6A, the detection portion 41 may be positioned between the one end of the separation roller 30 and the one of the side plates 32 b.

Referring to FIG. 5, the detection portion 41 may be L-shaped. The lower end of the detection portion 41 may be supported within the document conveying device 1 and may be configured to pivot, and the upper end may be a free end which is configured to project upward through the hole 22. The detection portion 41 may comprise an elastic member, such as a spring (not shown), and the detection portion 41 may be elastically biased upward to a side on which a document on the document positioning surface 14 c passes. The bias force of the elastic member may be selected, such that a document which contacts the upper end of the detection portion 41 readily may cause the detection portion 41 to pivot and retract into the hole 22, e.g., be positioned within the hole 22, such that detection portion 41 is positioned within hole 22 and is retracted from, i.e., does not project from, document positioning surface 14 c.

The detection portion 41 may be positioned, such that the lower end thereof may act as a shield between a light-emitting portion and a light-receiving portion of the photo interrupter 42. Consequently, referring to FIG. 6A, when the detection portion 41 pivots and retracts into the hole 22 in response to a force applied to the detection portion 41 by a document, a light beam emitted from the light-emitting portion of the photo interrupter 42 reaches the light-receiving portion, whereby the document sensor 40 may detect that the detection portion 41 has pivoted.

As such, when one or more documents are positioned on the document positioning surface 14 c of the feed tray 14, the leading ends of the documents pass below the pick-up roller 34 and are inserted until the leading ends contact the separation roller 30. In this case, the documents are positioned, such that the face of the document to be read faces upward. Referring to FIG. 6A, when one or more documents G1 are inserted and contact the detection portion 41 of the document sensor 40, the documents G1 apply a force to the detection portion 41, which causes the detection portion 41 to retract into the hole 22. As a result, the detection portion 41 pivots downward, whereby the photo interrupter 42 may detect the displacement of the detection portion 41. Consequently, it may be detected that the documents have been positioned on the document positioning surface 14 c of the feed tray 14.

When the document conveying device 1 receives a command to convey and read the documents from a manual operation of the control unit or from an external device, the separation roller 30 rotates and separates the uppermost document from the remaining documents, and then conveys the separated document to the conveying path 13. The reading unit 11 conveys the document with the face to be read facing downward. While passing the glass plate 6, the document may be read by the image reader 7. With the read face still facing downward, the document passes through the discharge unit 12 and is discharged to the discharge tray 15.

When one or more documents G2 positioned on the document positioning surface 14 c of the feed tray 14 are relatively thin sheets of paper and do not have sufficient rigidity to cause the detection portion 41 to retract into the hole 22, the documents G2 may be lifted upward from the detection portion 41. When the detection portion 41 is positioned outside of the casing 32, edges of the documents G2 lifted upward by the detection portion 141 may curl up and get caught by the drive shaft 131, resulting in jamming of the documents G2. As the number of relatively thin documents positioned on the feed tray 14 decreases, the likelihood that the documents will be lifted upward increases.

In addition, when the documents are relatively thin sheets of paper or the documents are curled or have wrinkles, the documents may be lifted upward by the detection portion 141 and may not be able to properly apply a force to the detection portion 141 to cause the detection portion 141 to pivot. This may result in a detection error or failure.

In contrast, in an embodiment of the present embodiment, the casing 32 may extend over the detection portion 41, such that one of the side plates 32 b of the casing 32 may be positioned relatively close to the detection portion 41. Moreover, the lower edges of the side plates 32 b may be closer to the surface of the feed tray 14 than the drive shaft 31. Consequently, as shown in FIG. 6B, even when the documents G2 are lifted upward by the detection portion 41, the side plate 32 b adjacent to the detection portion 41 may act as a presser for applying a force to the documents G2 toward the feed tray 14. Therefore, even when the documents G2 are relatively thin sheets of paper, the side plate 32 b acting as a presser substantially may prevent the documents G2 from getting caught by the drive shaft 31, thereby advantageously preventing jamming of the documents G2.

By reducing the uplift of one or more documents by means of the casing 32, the pivoting of the detection portion 41 in response to the force of the documents may be performed with greater reliability, which minimizes detection errors and may enhance the detection accuracy.

During operation, the separation roller 30 may be covered by the second cover 16, as shown in FIG. 4. Nevertheless, when a problem occurs in the feed unit 10, such as a paper jam, the user may open the second cover 16 and handle the separation roller 30 and its surrounding area. Referring to FIG. 3, in an embodiment of the present invention, the detection portion 41 of the document sensor 40 and the hole 22 through which the detection portion 41 may project are provided in an area that may be covered by the casing 32. Therefore, even when the user opens the second cover 16 and contacts the internal components, the user is unlikely to contact the detection portion 41. When an electric circuit board is positioned adjacent to the lower section of the detection portion 41, the electric circuit board may be damaged by electrostatic discharge if the user contacts the detection portion 41. Nevertheless, because the user is unlikely to contact the detection portion 41, the circuit board is unlikely to be damaged by electrostatic discharge.

In addition, because the casing 32 may extend over the detection portion 41 and the hole 22, through which the detection portion 41 may project, may have its upper opening covered by the casing 32, the hole 22 may be protected from dust and foreign particles. Consequently, the likelihood of short-circuit failure of the electric circuit board caused by dust and foreign particles may be significantly reduced.

Referring to FIG. 7A, a separation roller and a detection portion according to another embodiment of the present invention are depicted. The feed unit of this embodiment of the present invention is substantially similar to the feed unit 10 of the above-described embodiments of the present invention. Therefore, only those differences between this embodiment of the present invention and the above-described embodiments of the present invention are discussed with respect to this embodiment of the present invention. Similar to the above-described embodiments of the present invention, a detection portion 41 may be positioned within a casing 32, however, the detection portion 41 may be positioned between the both ends of a separation roller 30′. As shown in FIG. 7B, even when one or more documents G2 are relatively thin sheets of paper, a side plate 32 a applies a force to the documents G2 toward a feed tray 14 and prevents the document G2 from getting caught by a drive shaft 31.

As a document sensor that detects a document to be conveyed by the separation roller 30, the document sensor 40 is described in the above-described embodiments, as an example, which detects a document positioned on the document positioning surface 14 c of the feed tray 14 before the document is conveyed by the separation roller 30. Nevertheless, the document sensor is not limited to the document sensor 40. For example, a second document sensor having the same structure as the document sensor 40 may be positioned immediately downstream of the separation roller 30 and may be located within the casing 32. Specifically, the second document sensor may be configured to detect the leading end or the trailing end of a document conveyed by the separation roller 30. The second document sensor and the document sensor 40 may be provided in a side-by-side arrangement, or only one of the two sensors may be provided.

While the invention has been described in connection with embodiments, it will be understood by those of ordinary skill in the art that other variations and modifications of the embodiments described above may be made without departing from the scope of the invention. Other embodiments will be apparent to those skilled in the art from a consideration of the specification or practice of the invention disclosed herein. It is intended that the specification and the described examples only are considered as exemplary of the invention, with the true scope of the invention being defined by the following claims. 

1. A document conveying device comprising: a conveying path; and a feed unit comprising: a tray comprising a document positioning surface configured to receive at least one document thereon, wherein the document positioning surface has a hole formed therethrough; a separation roller which is rotatably supported by a drive shaft extending in a direction orthogonal to a document conveying direction and is configured to contact an uppermost document of the at least one document positioned on the document positioning surface and to separate and convey the uppermost document along the conveying path in the document conveying direction, wherein the separation roller comprises a first end and a second end opposite the first end; a document sensor comprising a detection portion configured to detect the at least one document positioned on the document positioning surface, and to selectively move between a first position in which the detection portion projects from the document positioning surface via the hole and a second position in which the detection portion is retracted from the document positioning surface via the hole; and a casing pivotably mounted on the drive shaft, wherein the casing comprises a plate extending adjacent to the first end of the separation roller in the document conveying direction, and the first end of the separation roller and the detection portion are positioned closer to the second end of the separation roller than the plate of the casing.
 2. The document conveying device of claim 1, wherein the separation roller comprises a first side and a second side opposite the first side, and the casing has an opening formed therethrough, wherein the separation roller is exposed to face the document positioning surface via the opening, and the casing is configured to cover at least the first side of the separation roller, wherein the second side of the separation roller faces the document positioning surface, and the casing extends over the detection portion.
 3. The document conveying device of claim 1, wherein a lower edge of the plate of the casing is positioned closer to the document positioning surface than the drive shaft is positioned to the document positioning surface.
 4. The document conveying device of claim 1, wherein the detection portion is positioned between the first end of the separation roller and the plate of the casing.
 5. The document conveying device of claim 1, wherein the separation roller and the casing are aligned with a first center line of the document positioning surface in a predetermined direction which is orthogonal to the document conveying direction, and are unaligned with a second center line of the document positioning surface in the document conveying direction.
 6. The document conveying device of claim 5, wherein the first end of the separation roller and the detection portion are positioned closer to the first center line of the document positioning surface than the plate of the casing.
 7. The document conveying device of claim 1, wherein the casing extends upstream from the drive shaft in the document conveying direction, and the document conveying device further comprises a pick-up roller rotatably coupled to the casing at an upstream side of the separation roller in the document conveying direction, wherein the pick-up roller is configured to contact the uppermost document.
 8. The document conveying device of claim 7, wherein the detection portion is positioned downstream of the pick-up roller and upstream of the separation roller in the document conveying direction.
 9. The document conveying device of claim 1, further comprising a cover configured to selectively move between an open position and a closed position in which the cover covers at least a downstream region of the tray in the document conveying direction, wherein the cover extends over the casing when the cover is in the closed position.
 10. An image reading device comprising: a document conveying device comprising: a conveying path; and a feed unit comprising: a tray comprising a document positioning surface configured to receive at least one document thereon, wherein the document positioning surface has a hole formed therethrough; a separation roller which is rotatably supported by a drive shaft extending in a direction orthogonal to a document conveying direction and is configured to contact an uppermost document of the at least one document positioned on the document positioning surface and to separate and convey the uppermost document along the conveying path in the document conveying direction, wherein the separation roller comprises a first end and a second end opposite the first end; a document sensor comprising a detection portion configured to detect the at least one document positioned on the document positioning surface, and to selectively move between a first position in which the detection portion projects from the document positioning surface via the hole and a second position in which the detection portion is retracted from the document positioning surface via the hole; and a casing pivotably mounted on the drive shaft, wherein the casing comprises a plate extending adjacent to the first end of the separation roller in the document conveying direction, and the first end of the separation roller and the detection portion are positioned closer to the second end of the separation roller than the plate of the casing. 